a. Field of the Invention
The present invention relates generally to apparatus for digging postholes and other small-diameter holes in the earth, and more particularly, to a hand-held posthole digger which forms bores in the earth by application of water pressure.
b. Related Art
Posthole diggers are used to bore comparatively small diameter holes in the earth, for installation of fence posts, and other posts and supports of various kinds. For purposes of convenience, the term "fence post", as used in this description will be understood to include all such supports and similar members, which are installed or otherwise placed so as to extend a few feet into the earth.
Although fence posts are, of course, widely used, they are particularly prevalent in the agricultural industries. For example, a typical livestock operation or orchard will have many hundreds or even thousands of fence posts, used for fences, to support trees or vines, and so on. Since the posts must be replaced or moved from time-to-time, the time and labor involved in installing fence posts becomes a major concern for many farmers, ranchers, orchardists, and so on.
Prior art posthole digging tools, however, have remained notoriously slow, labor-intensive, and inefficient in use. Manual posthole diggers have generally taken one of two forms: The most common comprises a pair of shovel-shaped blades which are joined together by a hinge, at the end of a pair of long poles; the operator thrusts the tool downwardly into the ground and then brings the blades together to withdraw a scoop of dirt. These tools are slow and tiring to use, and all the more inefficient due to their tendency to let dirt fall back into the hole as it is being withdrawn.
A second form of manual posthole digger uses a pair of auger like blades which define a bucket-like structure at the lower end of the tool, into which the dirt is scooped as the tool is rotated by the operator; after a few turns, the tool is lifted from the ground, dumped and the process is repeated. While superior in some respects to the type of tool described above, this latter form does not work well in rocky earth, and in any event remains an highly labor-intensive device.
Powered posthole diggers generally take the form of a long, screw-like auger mounted to a power head. Portable types are usually powered by a gasoline engine, and are comparatively fast in action. However, they are expensive, complicated, unreliable, and generally require two men in order to hold the power head against the torque which is generated by the bit during operation. These problems, especially the additional labor costs, represent serious drawbacks in commercial use.
Other types of posthole diggers are available which are designed to be mounted to a vehicle, such as a tractor or BOBCAT.TM. loader or similar vehicle for example. These devices are commonly driven using the vehicle's hydraulic system, and have the advantage of requiring only one operator. Again, however, they tend to be very expensive. Moreover, because they are mounted to the vehicle, this means that the vehicle must be maneuvered each time another hole is to be made, and in many instances there will not be enough room in which to maneuver the vehicle, as around trees or other obstacles. Once again, these drawbacks can present serious problems in a commercial operation, especially in the case of an orchard or a vineyard where many posts and other supports need to be placed in and amongst the plants themselves.
Accordingly, there exists a need for a posthole digger which is fast and efficient in operation, and which requires only a single operator, but which is also easily portable and convenient to use. Moreover, there exists a need for such a posthole digger which is simple and inexpensive in construction, and highly durable and reliable for extended use in a commercial operation.